Well, generally buildings provide enough rad protection for maps where the player and opposing majors aren't lobbing nukes at one another. The Anti-Rad Infrastructure could be useful for a front-line hex.
After looking over the tool tips for what the assets provide, it's probably best to think of the Rad Treatment Center as a Hospital or factory making rad-away, and Anti-Radiation Infrastructure as a concrete bunker.
It's still wholly unclear via the game's interface. ... and via the above explanation
For example, is the player to believe there is an area of effect? If so, how large? Is the treatment uniform? How does the player measure the asset's impact? Do these assets impact and reduce radiation of a hex/hexes or the units inside the hexes? Is the population changed or mutated in some way living inside radiation hexes?
Radiation is a half baked feature.
Asked back at launch per A Tale of Two Rad Treatments
A quick search will find that this ambiguity has been highlighted numerous times since launch.
I can't argue with that. The in game text on both facilities has two contradictory sayings. My explanation comes from the resource tooltip, not the facility description, and the dev comment in this thread. Almost looks like the in game text for the facilities should be switched, honestly.
The fact that radiation is immediately purged from a unit, rather than building up and killing them many turns later, is also unrealistic. But, I've rarely encountered a map where I even needed to bother with radiation. Frankly, I completely ignore it most of the time.